Propeller governor



PatentcdMar. 7, 1944 I PROPELLER GOVERNOR Eric Martin, West Hartford, com. assignor to United. Aircraft Corporation, East Hartford." Conn, a corporation of Delaware Application August 2, rose, Serial No. 287,874

6 Claims.

This invention relates to lmprovementsin hydraulic control means and has for an object the provision or an improved hydraulic control mechanism for a hydro-controllable aeronautical propeller.

An object of the invention resides in the provision of an improved control means for a hy- (ire-controllable propeller, operable in both directions by fluid pressure, so arranged that the fluid pressure tending to operate said propeller in one direction is greater when operativethan the pressure tending to operate the propeller in theopposite direction.

A further object resides in the provision of a control means for a hydro-controllable propeller utilizing hydraulic fluid at two difierent pressures, so arranged that one of said hydraulic,

pressures, will, whenever utilized, exceed the other of said hydraulic pressures by a predetermined amount.

A still further object resides in the provision of a control means for a hydro-controllable propeller utilizing hydraulic fluid in which such control means includes a pump for supplying hydraulic fluid to said propeller, and means for regulating the pressure of the fluid supplied by said pump to the varying pressure requirements of said propeller, thus obviating the necessity of maintaining the pump outlet pressure always at the maximum pressure required by said propeller and permitting the pump to operate at a'greatly reduced outlet pressure at all times except when the maximum pump pressure is required to change the propeller pitch.

Other objects and advantages will be more particularly pointed out hereinafter or will become apparent as the description proceeds.

In the accompanying drawing iniwhich like reference numerals are used to designate similar 'P rts throughout there is illustrated a suitable mechanical arrangement for the purpose of disclosing the invention; the drawing. however, is for the purpose of illustration only and is not to be taken as limiting or restricting the invention as it will be apparent'to those skilled in the art that various changes in the illustrated arrangement may be resorted to without in any way xceeding thescope oi" the invention.

In the drawing,

Fig. l is a diagrammatic illustration of a controllable-pitch propeller and a hydraulic control means constructed according to the invention various parts being shown in section to better illustrate the construction thereof. and

Fig. 2 is a vertical sectional view of an improved propeller control constructed according to the invention Referring to the drawing in detail, the numeral Ill generally indicates a propeller driving engine, from which projects a propeller drive shaft i2 upon which is mounted a hydro-controllable propeller generally indicated at It. The propeller has a plurality of blades, as indicated at I 6, rotatably mounted in a propeller hub I8 to which is secured a hydraulic pitch changing motor 20 including a piston 22 reciprocable in a cylinder 24 and operatively connected to the propeller blades by suitable means such as the intermeshing gears 26 and 28 for converting reciproeating movements of the piston 22 in the cylinder 28 into pitch changing movements of the blades 16. For a more detailed description 01' such a propeller, reference may be had to United States Patent No. 2,280,714, issued April 21, 1942, to Erle Martin for Feathering propeller control.

A tube so extends from'the engine lubricating system which is supplied with lubricating oil under pressure by the lubricating oil pump 32, through the hollow shaft l2 and motor 22 to the space between the motor 22 and closed end of the cylinder 24 remote from the engine. This lubricating oil may be withdrawn from a suitable reservcir such as the engine sump or oil tank 3t and the pressure oi the oil in the system may be.

regulated by a suitable pressure relief valve as generally indicated at 36 of some'form well known to the art. A plug 38 is disposed in the interior of the hollow shaft l2 surrounding the tube 30 to provide a second fluid channel leading to the motor 22 this channel comprising the interior of the hollow shaft surrounding the tube 30 on the propeller side of the plug 38. This construction provides two fluid channels leading to the propeller pitch changing motor, the first channel 303 leading to the pitch reducing side of the. motor and connected with the engine lubricating fluid at lubricating oil pressure to continuously supply fluid at this pressure to the pitch reducing side of the motor to assist the pction of centrifugal force on' the blade Ii in changing the propeller from a higher to a lower pitch condition while the channel comprising the interior of the hollow drive shaft surrounding thetube ll on the pro- -pelier side or the plug- 38 connects with the pitch of the hydraulic fluid shares to the pitch increasing side of the motor mufibe higher than the pressure of the fluid supplied to the pitch decreasing side by an amount sufficient to overcome the pressure of the hydraulic fluid on the pitch decreasing side and the effect of centrifugal force acting on the blade I6 tending to turn the blade toward a lower pitch, as well as the frictional resistance of the propeller blades and pitch changing motor. Y

Hydraulic fluid is supplied to the pitch increasing channel through a booster pump generally indicated at 40, which is connected with theoutlet of the lubricating oil pump 32 by a suitable conduit", a control valve actuated by the speed responsive governor, generally indicated at 66, a channel 46, conduit 50, bushing 62 surrounding the drive shaft, and ports 64 leading through the drive shaft from the exterior to the interior thereof on the propeller side of the plug 26.

The governor 46, as illustrated, is a centrifugal type governor having centrifugally actuated flyballs 66 which react against a compression spring 66 through a suitable thrust bearing 60. The speeder spring 58 may be adjusted by a suitable or conventional means, as indicated at 63, to change the speed setting of the governor. The flyballs 66 are driven from the'engine through the hollow drive shaft 62, which has a driving connection with the engine, such as'the gear drive generally indicated at 64 in Fig. 1, to which the shaft may be connected by a suitable spline drive 66, so that changes in engine speed change the action of centrifugal force on the flyballs 66 resulting in a movement of the thrust bearing 60 and a consequent movement of the valve plunger 66 in the hollow shaft 62. The plunger 66 is provided with spaced valve pistons I0, 12 and 14 separated by reduced portions providing annular fluid spaces between the pistons. The plunger is provided with an internal channel I6 leading from a port 18 between the pistons and 12 to a port 06 below the piston I4, the reduced end portion of the plunger below the port 60 being closed.

The hollow drive shaft 62 is provided with two rings of ports or apertures, as indicated at 62 and 66, which lead into respective annular channels 66 and 68 provided in the governor housing 60 surrounding the bore provided in the housing for the drive shaft 62. The pistons 10, I2 and H and the ports 62 and 64 are so disposed as to provide a valve action within the movement limits of the governor 66 such that when the plunger 60 is moved upwardly, incident to an engine speed in excess of the' speed for which the governor is set, the piston 12 will be above the port 62 and piston I4 below the port ll thereby connecting these ports through the reduced portion of the valve plunger so that hydraulic fluid will flow directly from the annular channel 66 into the anengine is below the speed for which the governor is set, the ports 02 will be between the pistons 10 and 12 and the port 04 between the pistons I2 and I4 under which condition the channel 86 will be blocked and the channel 66 will be connected through the plunger port 16, the internal arent that when the valve plunger i in the. up-'- nular channel 86 and, when'the speed of the per position connecting the annular channels 88 and 00 hydraulic fluid under high pressure will be supplied to the propeller pitch changing motor to increase theqiitch of the propeller, and when the plunger is in its lower position the pitch increasing side of the pitch changing motor will be connected with drain and the pitch of the propeller will be reduced by the pressure of the hydraulic fluid admitted to the pitch reducing side of the motor through the tube 30 in cooperation with the pitch reducing action of centrifugal force on the propeller blades I 6; It has been found desirable to close the lower end of the valve plunger 68 and have the drain fluid flow laterally from the plunger through the port, or ports in order to avoid any disturbing force on the plunger by the jet action of the fluid occasioned by discharging the fluid in line with the plunger movements.

The booster pump 40 may conveniently comprise a gear element 92 formed integrally with or rigidly secured to the drive shaft 62 and a oooperating gear element 9| meshing with the gear 92 and having anintegral or rigidly attachedhollow axle 96 supported in a bore provided in the governor base 98 and lower portion of the housing 90. These gears are disposed in suitable recesses provided in the base 98 which constitute in effect the pump casing. The hydraulic fluid inlet from the pump 32 through the conduit" may include the groove I00 in the lower surface of the casing and the channel I02 schematically shown in Fig. 1. The pump outlet is connected through a channel I04, schematically shown in Fig. 1, with a pressure chamber I06 which pressure chamber communicates, under certain conditions, through the hollow axle 96 of the gear 96 with the pump inlet so that fluid may be recirculated through the pump when the fluid line to the propeller is blocked by the valve plunger 68 in the manner indicated above. For a more detailed description and illustration of the booster pump inlet and outlet channels reference may be had to United States Patent No. 2,204,640, issued June 18, 1940, to Elmer E. Woodward, for Governor mechanism.

The connection between the pressure chamber I06 and the return to the pump inlet through the axle 86 is controlled by a pressure relief valve,

generally indicated at I08, which regulates the low plunger IIO slidably mounted in the end of the pressure chamber remote from the drive shaft 62, a compression spring '2 for urging the plunger to valve closing position and a screw threaded nut lIl constituting a flxed rear abutment for the spring. When the plunger I06 is in the position illustrated in Fig. 2 the relief valve is closed. If the pressure in the chamber I06 exceeds a predetermined value the plunger II 0 will be forced to the right, as viewed'in Fig. 2. until its closed end passes beyond the left hand side of the chamber II6 whichcommunicates with the interior of the hollow axle 96. When the plunger is in this last described position the ressure chamber I06 will be connected with the intake of the pump 40 through the hollow axle 96 and groove I00 and the pressure of the hydraulic fluid in the chamber will be reduced by the venting of a portion of the fluid to the pump intake. If desired, a suitable stop for the left hand movement of the valve plunger, as viewed in Fig. 2, may be provided in the form of an The spring 2 is made very light, theoreti cally having only suflicient strength to overcome the frictional resistance of the plunger, and to resiliently urge the plunger toward its valve closing position. In order to insure the performance of the theoretical requirements, in actual practice the spring H2 is made strong enough to close the valve against a small hydraulic head. In certain commercial installations a spring requiring 50 pounds per square inch pressure to open the valve has been found satisfactory. With this arrangement, when'no additional force is exerted to maintain the plunger in its valve closing position the load on the pump 40 will be reduced since it will be pumping only against the hydraulic head necessary to overcome spring i i2. When the port 62 is blocked by piston 12 and the blades are thereby held against pitch changing movements, the pump will be working against the hydraulic head'necessary to overcome spring H2 and the hydraulic head created by the effect of the blade centrifugal twisting moment on the oil trapped in th propeller and acting on the. rear of the plunger H8. These conditions can exist at all times at which the booster pump as is not supplying hydraulic fluid under pressure to the pitch increasing side of the pitch changing motor 22 for changing the propeller pitch.

pressure must be increased by an amount sufiicient to overcome the inertia and frictional forces opposing a change of propeller pitch. A channel I20 is Provided through the governor housing 8|! leading from the annular channel 86 to the space in the valve bore at th rear'of the piston ilil so that when the channel 86 is connected with the booster pump outlet through the channel 88 and pressure chamber I06, hydraulic fluid under the booster pump pressure will be carried to the rear of the relief valve "plunger to add its force to the force exerted by the spring 2.. Since the pressure in the annular channel 8E is controlled by the rate of flow of hydraulic fluid to the pitch changing motor and this rate of flow is determined largely by the resistance encountered by the motor in changing the propeller pitch, the pressure developed by the pump to will be limited substantially to that necessary to change the propeller pitch. Under these conditions a hydraulic pressure could be built up in the pressure chamber Hi8 limited only by the capacity of the pump at. Hhwever, a channel I22 is provided leading from the space at the rear of the relief valve plunger Ho through a second pressure relief or blowoif valve, generally indicated at 24, and a channel I28 connects this valve with the pump inlet or drain to limit the maximum pressure which can be developed by the booster pump and pressure relief valve com* bination. This pressure limiting valve I24 may be of any conventional or desired form but may conveniently be provided as a ball check valve having a ball I28 urged to seating position against the end or the channel I22 by a compression spring I30 held in a bore I32 provided in the governor base 98 by a screw threaded plug I36. With this construction the strength of the spring I30 will determine the maximum pressure which the booster pump can build up in the pressure chamber I06 and in the pitch changing motor of the propeller. A spring will be selected having a strength which will permit the fluid to escape from the space behind the relief valve piston Ill before fluid pressures are reached which would endanger the structure or the pitch changing motor or the control therefor or the connecting conduit. Whenever the piston 12 of the plunger 68 is below the port 82, the space at the rear of the relief valve plunger III! will be vented to drain through the channel 86' and the internal passage 16 of the pilot valve plunger 68 so that the only force acting on the plunger l 0 will be that of the spring I I 2.

From the above description it will be observed that there has been provided an arrangement in When such fluid is supplied the which the pitch changing motor of a controllable-pitch propeller is actuated in one direction by hydraulic fluid at one pressure to assist centrifugai action acting on the blades in reducing the pitch of the propeller and in which the pitch changing motor is actuated to increase the propeller pitch by hydraulic fluid at a pressure high-.

er than said one pressure by an amount suiflcient to overcome the force exerted by the hydraulic fluid at said one pressure and the effect of centrifugal action on the blades plus the frictional resistance of the propeller blades and pitch changing motor, and in which the higher pressure of the hydraulic fluid is developed by a booster pump which operates under load only during those intervals in which the propeller pitch'is' being increased and in which the pressure developedby the pump is only suflicient to accomplish the indicated pitch change, thereby saving wear and tear on the booster pump and preventing this pump from absorbing engine power unnecessarily when its function is not being utilized.

While a particular mechanical arrangement has been hereinabove described and illustrated in the accompanying drawing for the purpose of disclosing the invention, it is to be understood that the invention is not limited to the arrangemerit so illustrated and described but that such changes in the size, shape and arrangement of the various parts may be resorted to as come within the scope of the sub-joined claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. In a control for a hydro-controllable propeller, a pitch changing motor operated by hydraulic fluid under pressure, a speed responsive governor, a pump for creating said pressure, a pilot valve operated by said governor and connecting one side of said pitch changing motor withthe outlet of said pump or with a drain vent, a pressure relief valve permanently connected to said pump outlet and urged to open position by the pump created fluid pressure for limiting the pressure which may be developed by said pump, and a channel, controlled by said pilot valve, and connected with the outlet of said pump when said pilot valve is in position to apply pressure fluid to said motor, for conducting pressure fluid to the rear 01' said pressure relief valve to urge said pressure relief valve to closed position and vented to drain when said pilot valve is in position to vent said one side of said motor, to relieve the pressure urging the valve to closed position.

2..In a control for a hydro-contro lable proa pump for supplylower pressure, a

governor controlling the application of hydraulic fluid at said higher pressure to one side of said pitch changing motor and alternatively venting said one side of said pitch changing motor, and a channel connected with said one side of said motor and said second pressure relief valve leading hydraulic fluid to the back of said second pressure relief valve to apply a valve closing force in addition to the force of said spring proportional to the fluid pressure in said one side of said pitch changing motor.

3. In a control for a hydro-controllable propeller, a pitch changing motor operable in one direction by hydraulic fluid under pressure and operable in the opposite direction, a booster pump for creating said pressure, a pressure chamber connected with-the outlet of said pump, means connecting said chamber with said pitch changing motor, a speed responsive governor, a governor actuated valve in said connecting means for controlling the application oi! hydraulic fluid to said motor, and a pressure relief valve connected with said chamber for controlling the pressure in said pressure chamber comprising, a cylindrical bore, a plunger reciprocable in said bore operative to block the flow of fluid from said chamber when in valve closing position and to vent fluid fromsaid chamber to a drain when in valve opening position, a passage between said governor actuated valve and said motor connectible by said governor actuated valve with the outlet of a pump or with said drain and a channel leading from said passage to the space within said bore at the side of said plunger remote from said chamber for applying the hydraulic pressure in said passage to said plunger to urge said plunger to valve closing position.

4. In a propeller pitch control comprising a fluid actuated motor for changing the propeller pitch, a pump driven with said propeller for supplying fluid under pressure, a governor driven with said propeller, a governor actuated valve connecting said motor with said pump or with an outlet and controlling the flow of said fluid under pressure from said pump through a pressure line to said motor or connecting said motor with said outlet, a pressure relief valve having one side operatively connected with said pump, and means for normally urging said valve to closed position to maintain a predetermined pressure on said fluid under pressure; means for varying the relief valve setting in accordance with the requirements of the fluid actuated motor comprising a permanently open connection connecting the other side of said relief valve with said pressure line for supplying fluid to said relief valve in a direction to urge said valve to a closed position.

5. In a control for a hydro-controllable propeller, a hydraulic pitch changing motor having different fluid pressure requirements for difierent speeds and pitch angles of said propeller, a fluid pump driven with said propeller for supplying hydraulic fluid under pressure to said motor, a

fluid connection between the outlet of said pump and said motor, a speed governor driven with said propeller, a valve operated by said governor and interposed in said fluid line and having a drainconnection for connecting said motor with either fluid under pressure or with a drain to change the pitch of said propeller in response to speed change demands of said governor, and a relief valve for said pump intercepting a drain channel leading from said pump outlet and urged to channel closing position by the fluid pressure in the portion of said fluid connection between said governor operated valve and said pitch changing motor to maintain the pump outlet pressure proportional to the fluid pressure requirements of said pitch changing motor.

6. In a control for a hydro-controllable propeller, a speed governor and a hydraulic pump driven with said propeller, a hydraulic pitch changing motor, a fluid connection between said pump and said motor, a governor operated valve intercepting said connection and operative to connect said motor with the outlet of said pump or with a drain, a fluid passage between the outlet and inlet of said pump, a pressure relief valve intercepting said passage including a piston movable to a position blocking said passage and urged by the pump outlet pressure to a position opening said passage, a fluid channel connecting said relief valve with the portion of said fluid connection between said governor operated valve and said pitch changing motor' to apply the pressure of the fluid entering or leaving said motor to said relief valve plunger to urge said plunger to a passage blocking position, and a light spring resiliently urging said plunger to a passage blocking position.

ERLE MARTIN. 

